Allogeneic stem cell transplantation in the treatment of acute myeloid leukemia: An overview of obstacles and opportunities

Table 2 Main factors for post-transplant immune reconstitution

Factors	Effect	Ref.
Recipient age	Several studies show that immune reconstitution, especially the reconstitution of CD4+ T cells, is inversely related to age. However, some studies report that age has no effect on the reconstitution of any subgroup of lymphocytes	[63,90,91]
Graft source	Immune reconstitution occurs faster after PBSCT than after BMT. This may be because PBSCT grafts are rich in mature lymphocytes. Delayed immune reconstitution after UCBT is related to low lymphocyte count and immature immune cells in umbilical cord blood	[61,92-95]
HLA matching between donor and recipient	HLA mismatch causes delayed reconstitution of neutrophils and T cells
Intensity of preconditioning	Several studies show that compared with MA-SCT, RICSCT reduces thymus damage and promotes immune reconstitution. However, some studies show no significant difference in recipient immune reconstitution between these two transplantation methods	[60,96-98]
GVHD	GVHD damages thymus structure and function and interferes with T cell differentiation at all stages, thereby affecting T cell reconstitution. GVHD also affects the recovery of B cell number and function	[84,99]
GVHD prevention	Donor TCD reduces the risk of GVHD; however, the lack of T cells increases the risk of infection and delayed immune reconstitution	[100]
	The use of ATG or alemtuzumab has a negative effect on the reconstitution of T cells and B cells	[101-103]

ATG: Antithymocyte globulin; BMT: Bone marrow transplantation; CD4: Cluster of differentiation 4; GVHD: Graft-versus-host disease; HLA: Human leukocyte antigen; MA-SCT: Myeloablative stem cell transplantation; PBSCT: Peripheral blood stem cell transplantation; Ref.: Reference; RICSCT: Reduced-intensity conditioning stem cell transplantation; TCD: T cell depletion; UCBT: Umbilical cord blood stem cell transplantation.